1. Field of the Invention
The present invention relates to a water level sensing unit, a steam generator having the water level sensing unit, and a heating cooking apparatus having the steam generator, and, more particularly, to a water level sensing unit having an improved structure to reliably sense variations in the level of water even when a large amount of scale exists, a steam generator having the water level sensing unit, and a heating cooking apparatus having the steam generator.
2. Description of the Related Art
Examples of general heating cooking apparatuses used to cook food include a microwave oven using a high frequency, and a gas oven and an electric oven designed to directly apply heat to food using a heater. Of the above-mentioned heating cooking apparatuses, the microwave oven is greatly limited in the kind of food cooked therein and suffers from deterioration in the taste of the cooked food because of excessive drying of the food. Also, the gas oven and the electric oven have problems of excessively long cooking time and low cooking efficiency because they use air having a relatively low density as a heat transfer medium between the heater and food to be cooked.
Recently, as a solution to the above described problems of the conventional heating cooking apparatuses, a heating cooking apparatus (hereinafter, referred to as “steam oven”) has been developed. The steam oven is designed to heat food using steam. When cooking food using the steam oven, it is possible to maintain an appropriate amount of moisture in food and consequently, maintain the original taste of food. Also, steam filling up a cooking compartment of the oven acts as an efficient heat transfer medium, resulting in a reduction in cooking time.
The steam oven generally includes a steam generator to generate and supply steam by heating water, and a water supply device to supply water into the steam generator. The steam generator includes a steam container to provide a steam generation space therein, and a steam heater to heat water supplied into the steam container. The water supply device includes a water vessel, and a water supply pump to transfer water stored in the water vessel into the steam container.
The water pump is adapted to stop operation thereof after supplying a predetermined amount of water into the steam container, and the steam heater is adapted to generate steam by heating the water supplied into the steam container when power is applied thereto. The generated steam is supplied into a cooking compartment of the oven through a steam supply tube that connects the steam container to the cooking compartment. The amount of water filled in the steam container is reduced as the steam is discharged. If all the water in the steam container is evaporated and thus, the supply of steam is stopped, efficient cooking of food is not possible any more and overheating of the steam heater may result in damage to the steam generator as well as unwanted accidents. Therefore, in the case of the steam oven, water should be continuously supplied to the steam container whenever the level of water in the steam container is lowered below a predetermined level.
For this, a water level sensing unit is installed in the steam container and adapted to sense the level of water in the steam container, such that the water supply pump is operated in response to a signal from the water level sensing unit, to achieve automatic supply of water. Accordingly, it is important to accurately sense variation of the level of water in the steam container during the generation of steam for stable and safe operation of the steam oven without the risk of accidents.
Conventionally, there has been generally used a water level sensing unit wherein a float, which is made of foamed polypropylene (PP) material, is installed around a center shaft that is installed orthogonal to the surface of water so that the float is movable up and down according to variation of the level of water. The float has a magnet, and the center shaft has a magnetic sensor to sense a magnetic force of the magnet. Thereby, the magnetic sensor senses positional variation of the magnet depending on the level of water, thus sensing variation of the level of water.
However, the above-described conventional water level sensing unit has a problem in that the float made of foamed polypropylene material eventually absorbs an excessive amount of water. The soaked float has difficulty performing efficient upward and downward movements thereof and may fail to accurately sense variation of the level of water.
Furthermore, the steam container suffers from scale caused therein as steam is generated. The scale acts to prevent efficient upward and downward movements of the float as scale sticks to the float or center shaft, thereby preventing the sensor from accurately sensing variation of the level of water.